Method of manufacturing cast iron components for industrial equipment

ABSTRACT

Methods of manufacturing cast iron components having increased hardness are disclosed herein. In an example embodiment, a method of forming a cast iron component for industrial equipment includes forming the cast iron component in a predetermined shape, machining the cast iron component, heat treating the cast iron component by raising the temperature of the cast iron component to an upper temperature, and cryogenically heat treating the cast iron component by lowering the temperature of the cast iron component to a lower temperature.

PRIORITY

This application claims priority to U.S. Provisional Application No. 63/237,203, filed Aug. 26, 2021, entitled “Method of Manufacturing Cast Iron Components for Industrial Equipment”, the entire contents of which is incorporated herein by reference and relied upon.

BACKGROUND Field of the Invention

The present disclosure relates to a method of manufacturing cast iron components for industrial equipment. More specifically, the present disclosure relates to a method of manufacturing a high-strength cast iron pump impeller or other cast iron component.

Background of the Invention

High pressure fluid movement is required in various industries, for example, industries which revolve around or require industrial equipment for mining, milling, earth-handling or manufacturing. The pumps used by these types of industries are often required to move large volumes of high viscosity material at high rates. This requires pump impellers made of high strength materials which are not susceptible to breakage.

SUMMARY

It has been determined that existing methods of manufacturing cast iron components can be improved to increase the strength of the components (e.g., pump impeller) after being formed and machined. The methods discussed herein allow the cast iron components to be formed in desired shapes, machined, and still maintain a desirable hardness when complete. This leads to increased durability and run time, which reduces product failure and replacements resulting in a massive advantage in the field of pump impellers.

In view of the state of the known technology, a first aspect of the present disclosure is to provide a method of forming a cast iron component for industrial equipment. The method includes forming the cast iron component in a predetermined shape, machining the cast iron component, heat treating the cast iron component by raising the temperature of the cast iron component to an upper temperature, and cryogenically heat treating the cast iron component by lowering the temperature of the cast iron component to a lower temperature.

In another aspect of the disclosure, which can be combined with any other aspect described herein, the lower temperature is at or below 0° C.

In another aspect of the disclosure, which can be combined with any other aspect described herein, the upper temperature is at or above 950° C.

In another aspect of the disclosure, which can be combined with any other aspect described herein, cryogenically heat treating the cast iron component includes lowering the temperature of the cast iron component to between about −70° C. and −80° C.

In another aspect of the disclosure, which can be combined with any other aspect described herein, cryogenically heat treating the cast iron component includes maintaining the cast iron component at about the lower temperature for between about 2 to 4 hours.

In another aspect of the disclosure, which can be combined with any other aspect described herein, the method includes stress relieving the cast iron component before machining the cast iron component.

In another aspect of the disclosure, which can be combined with any other aspect described herein, forming the cast iron component includes forming the cast iron component as a single piece.

In view of the state of the known technology, another aspect of the present disclosure is to provide a method of improving the hardness cast iron components for industrial equipment. The method includes forming a first cast iron component into a predetermined shape using a first liquid mixture, the first cast iron component having a first hardness, increasing a concentration of at least one element in a second liquid mixture in comparison to the first liquid mixture, forming a second cast iron component into the predetermined shape using the second liquid mixture, the second cast iron component having a second hardness greater than the first hardness, and further increasing the second hardness of the second cast iron component by cryogenically heat treating the second cast iron component by lowering the temperature of the cast iron component to a lower temperature.

In another aspect of the disclosure, which can be combined with any other aspect described herein, the at least one element is carbon.

In another aspect of the disclosure, which can be combined with any other aspect described herein, the at least one element is molybdenum.

In another aspect of the disclosure, which can be combined with any other aspect described herein, the method includes adding niobium to the second liquid mixture.

In another aspect of the disclosure, which can be combined with any other aspect described herein, the method includes heat treating the first cast iron component by raising the temperature of the first cast iron component to a first temperature for a first duration, and heat treating the second cast iron component by raising the temperature of the second cast iron component to a second temperature for a second duration, the second temperature being lower than the first temperature.

In another aspect of the disclosure, which can be combined with any other aspect described herein, the method includes heat treating the first cast iron component by raising the temperature of the first cast iron component to a first temperature for a first duration, and heat treating the second cast iron component by raising the temperature of the second cast iron component to a second temperature for a second duration, the second duration being less than the first duration.

In another aspect of the disclosure, which can be combined with any other aspect described herein, machining the first cast iron component at a first location, and machining the second cast iron component at the first location.

In view of the state of the known technology, another aspect of the present disclosure is to provide a method of improving the hardness cast iron components for industrial equipment. The method includes forming a first cast iron component into a predetermined shape using a first liquid mixture, heat treating the first cast iron component by raising the temperature of the first cast iron component to a first temperature for a first duration, the first cast iron component having a first hardness after heat treatment, forming a second cast iron component into the predetermined shape using a second liquid mixture, heat treating the second cast iron component by raising the temperature of the second cast iron component to a second temperature for a second duration, the second cast iron component having a second hardness after heat treatment, the second hardness greater than the first hardness, at least one of the second temperature being lower than the first temperature and/or the second duration being less than the first duration, and further increasing the second hardness of the second cast iron component by cryogenically heat treating the second cast iron component by lowering the temperature of the cast iron component to a lower temperature.

In another aspect of the disclosure, which can be combined with any other aspect described herein, the method includes increasing a concentration of at least one element in a second liquid mixture in comparison to the first liquid mixture.

Also, other objects, features, aspects and advantages of the disclosed system and method will become apparent to those skilled in the art in the pump impeller field from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of pump impeller strengthening methods with various features.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail hereinafter with reference to the drawings.

FIG. 1 illustrates an example embodiment of a method for manufacturing a cast iron component for industrial equipment according to the present disclosure;

FIG. 2 illustrates an example embodiment of a cast iron component which can be manufactured using the methods of the present disclosure;

FIG. 3 illustrates two samples of white cast iron to demonstrate the advantages of the methods of the present disclosure;

FIG. 4 illustrates the microstructure of the white cast iron samples from FIG. 3 ;

FIG. 5 further illustrates the microstructure of the white cast iron samples from FIG. 3 ; and

FIG. 6 illustrates an example embodiment of a method for increasing the hardness cast iron components for industrial equipment according to the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Selected embodiments will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

FIG. 1 illustrates an example embodiment of a method 10 for manufacturing a cast iron component 30 for industrial equipment. FIG. 2 illustrates an example embodiment of a cast iron component 30. As described in more detail below, the method 10 includes a two-step heat treatment which improves the overall hardness of the cast iron component 30 after the cast iron component 30 has been formed and machined. It should be understood by those of ordinary skill in the art from this disclosure that certain steps of the method 10 can be added, omitted or modified without departing from the spirit or scope of this disclosure.

In the illustrated embodiment show in FIG. 2 , the cast iron component 30 is a pump impeller 32. The impeller 32 includes a first end 34 and a second end 36. The first end 34 of the pump impeller 32 includes a shaft 38 which extends along a central axis. The second end 36 of the pump impeller 32 includes a plurality of vanes 40 which extend radially outward from the shaft 36 with respect to the central axis. During manufacture, the shaft 38 and/or vanes 40 can require additional machining. The vanes 40 in particular are susceptible to breakage during use, for example, when operating at high rates and/or moving large volumes of high viscosity material. It should be understood by those of ordinary skill in the art from this disclosure that the pump impeller 32 shown in FIG. 2 is an example only and that pump impellers can be formed in various shapes and sizes according to the method 10 of the present disclosure. It should further be understood by those of ordinary skill in the art from this disclosure that the cast iron component 30 can take other forms, for example, those of other cast iron components in industrial equipment which require enhanced hardness.

The methods described herein are particularly advantageous when used to manufacture or otherwise improve a pump impeller or rotor to be used with Eddy Pump equipment, for example, as shown and described in the Eddy Pump Corporation's U.S. patents and publications. In an embodiment, the pump impeller 32 is a pump impeller or rotor as shown or described in one or more of U.S. Pat. Nos. 10,480,524 and 10,883,508 and U.S. Publication Nos. 2018/0142691 and 2019/0383305, the structure and requirements of each of which are incorporated herein by reference. The industrial equipment described herein can thus include the Eddy Pump equipment described in these patents and publications.

The cast iron component 30 is formed as a single piece of cast iron. More specifically, in the illustrated embodiment of the pump impeller 32, the shaft 38 and plurality of vanes 40 are formed as a single piece of cast iron. In the illustrated embodiment, the cast iron is white cast iron. As should be understood by those of ordinary skill in the art from this disclosure, white cast irons are hard and brittle, but cannot be easily machined. The method 10 discussed herein allows the white cast iron to be formed and machined while having an improved hardness at the end of the process.

FIG. 3 illustrates two samples of white cast iron. Sample 1 is made from an alternative process in comparison with the method 10 disclosed herein, while Sample 2 is made from the method 10 disclosed herein excluding step 20. Sample 1 has an increased hardness versus Sample 2, whereas Sample 2 is easier to machine that Sample 1. The method 10 described herein allows for the machining capability of Sample 2 with equal or greater hardness than that of Sample 1.

FIGS. 4 and 5 show the microstructure of Samples 1 and 2. As illustrated in FIG. 4 , the majority of the matrix of Sample 1 is martensite, and there is minimal austenite. Conversely, the majority of the matrix of Sample 2 is austenite, and there is minimal martensite. Sample 1 also contains more eutectic carbides than Sample 2. As illustrated in FIG. 5 , Sample 1 also includes many more metal carbide precipitates that are smaller than those of Sample 2, which has less metal carbide precipitates that are much bigger. The result of these factors is that Sample 1 is harder and more abrasion resistance than Sample 2. However, Sample 1 is also more difficult to machine than Sample 2.

Table 1 shows the chemical compositions of Samples 1 and 2 in comparison to the ASTM A532 standard. The ASTM A532 standard covers a group of white cast irons that have been alloyed to secure high resistance to abrasive wear for applications such as mining, milling, earth-handling, and manufacturing. The chemical compositions of Samples 1 and 2 in Table 1 were determined by X-ray fluorescence (XRF) and combustion methods per ASTM 1019.

TABLE 1 Chemical Composition (weight %) Sample 1 Sample 2 ASTM A532 Carbon 2.8 2.1 2.0-3.3 Chrome 27.4 25.3 23-30 Molybdenum 0.6 0.4 3.0 max Nickel 0.6 0.1 2.5 max Manganese 0.7 0.4 2.0 max Silicon 1.1 0.9 1.5 max Sulphur 0.04 0.03 <0.06 Phosphorus unknown unknown 0.10 max 

As shown, Sample 2 has a lower overall carbon concentration in comparison to Sample 1, leading to the decreased martensite shown in FIG. 3 . Sample 2 also has a lower concentrations of chrome, molybdenum, nickel, manganese, silicon and sulphur.

Table 2 shows the Rockwell “C” Scale hardness of Samples 1 and 2 in comparison to the ASTM A532 standard.

TABLE 2 ASTM A532 Hardened and Sample 1 Sample 2 Stress Relieved Hardness 58.7 56.9 59 min Rockwell “C” Scale

As illustrated, neither Sample 1 nor Sample 2 meet the ASTM A532 standard, although Sample 1 is closer than Sample 2. Although more easily machined, Sample 2 has a lower hardness than Sample 1 and the minimum required to meet the ASTM A532 standard. The method 10 disclosed herein strengthens Sample 2 to meet or exceed the hardness of Sample 1 and the ASTM A532 standard. The method 10 disclosed herein thus allows a cast iron component 30 (e.g., pump impeller 32) to be formed and machined with the resulting product meeting or exceeding the ASTM A532 standard.

Referring again to FIG. 1 , at step 12 of the method 10, the cast iron component 30 is formed into a predetermined shape. More specifically, the cast iron component 30 is cast into a predetermined shape using one or more molds. In an embodiment, the cast iron component 30 is cast as a single piece. In an embodiment, the predetermined shape of the cast iron component 30 can be that of a part for industrial equipment. In an embodiment, the predetermined shape can be that of a pump impeller 32. In an embodiment, the pump impeller 32 can include a shaft 38 and a plurality of vanes 40 that are cast as a single piece. Those of ordinary skill in the art will understand from this disclosure that various casting processes and/or shapes can be used with the method 10 discussed herein.

In an embodiment, forming the cast iron component 30 includes smelting iron ore. In an embodiment, forming the cast iron component 30 includes mixing iron ore with alloys to create a liquid mixture. In an embodiment, forming the cast iron component 30 includes pouring the liquid mixture into one or more molds. The one or more molds define the predetermined shape of the cast iron component 30. In an embodiment, forming the cast iron component 30 includes allowing or causing the liquid mixture to cool and solidify within the one or more molds. More specifically, the liquid mixture cools and solidifies so that the cast iron component 30 is a single piece. Once the cast iron component 20 has solidified, the molds can be removed.

At step 14 of the method 10, a stress relief process is performed on the cast iron component 30. In an embodiment, stress relieving the cast iron component 30 includes soaking the cast iron component 30. In an embodiment, stress relieving the cast iron component 30 includes a heating portion and a cooling portion. In an embodiment, the heating portion includes heating the cast iron component 30 to between 550° C. and 650° C. In an embodiment, the cooling portion includes furnace cooling. In an embodiment, the cooling portion includes cooling the cast iron component 30 to a temperature less than about 100° C. Those of ordinary skill in the art will understand from this disclosure that other stress relieving processes can also be used.

At step 16 of the method 10, the cast iron component 30 is machined. In an embodiment, the pump impeller 32 is machined for a specific application. For example, the shaft 38 and/or vanes 40 are machined for a specific application. In an embodiment, the shaft 38 is machined to mate with another part of a pump. In an embodiment, the vanes 40 are machined to affect fluid flow, for example, when operating at high rates and/or moving large volumes of high viscosity material. In an embodiment, the cast iron component is machined at one or more particular locations, for example, a first location, a second location, etc.

In an embodiment, machining the cast iron component 30 includes milling the cast iron component 30 using a milling machine. In an embodiment, the milling machine includes a cutting edge which can be used to machine the cast iron component 30. In an embodiment, the milling machine can have multiple cutting edges. In an embodiment, the cast iron component is milled at one or more particular locations, for example, the first location, the second location, etc. Those of ordinary skill in the art will understand from this disclosure that other machining processes can also be used.

At steps 18 and 20 of the method 10, the cast iron component 30 undergoes a two-step heat treatment which improves the overall hardness of the cast iron component 30 after the cast iron component 30 has been formed and machined. At the first step of the two-step heat treatment, step 18, the temperature of the cast iron component 30 is raised to at or above an upper temperature. At the second step of the two-step heat treatment, the temperature of the cast iron component 30 is lowered below a lower temperature.

At step 18 of the method 10, the cast iron component 30 receives heat treatment in which the temperature of the cast iron component 30 is raised to at or above an upper temperature. More specifically, the cast iron component 30 receives a destabilizing heat treatment. The destabilizing heat treatment destabilizes the austenite of the cast iron component 30. In an embodiment, the upper temperature is about 950° C., such that the cast iron component 30 is raised to at or above about 950° C. In an embodiment, the upper temperature is between about 950° C. and about 1150° C. Those of ordinary skill in the art will understand that the upper temperature can vary within this range depending on the particular cast iron component 30 being manufactured.

In an embodiment, the heat treatment at step 18 includes a heating portion and a quenching portion. The heating portion includes heating the cast iron component 30 to an upper temperature that is a predetermined temperature or within a predetermined temperature range. In an embodiment, the heating portion includes heating the cast iron component 30 to a predetermined temperature between about 950° C. and about 1150° C. In an embodiment, the quenching portion includes air quenching the cast iron component 30.

At step 20 of the method 10, the cast iron component 30 undergoes a heat treatment in which the temperature of the cast iron component 30 is lowered to at or below a lower temperature. More specifically, the cast iron component 30 undergoes a cryogenic heat treatment. In an embodiment, the lower temperature is below 0° C., or more preferably at about −76° C. In an embodiment, the cast iron component 30 is placed in a cryogenic chamber. In an embodiment, the cryogenic heat treating of the cast iron component 30 includes maintaining the cast iron component 30 at below 0° C. for a duration of time. In an embodiment, the cast iron component 30 is maintained at between about −50° C. and −100° C., preferably between about −60° C. and −90° C., more preferably between about −70° C. and −80° C., more preferably at about −76° C. In an embodiment, the cast iron component 30 is maintained at this lower temperature for between about 2 to 4 hours, more preferably for about 3 hours. Thus, in an embodiment, the cast iron component 30 is maintained at about −76° C. for 3 hours within the cryogenic chamber.

In an embodiment, the method 10 can be used to improve the hardness of cast iron components for industrial equipment. FIG. 6 illustrates an example embodiment of a such a method 50 for improving the hardness of cast iron components for industrial equipment. The method 50 can be used, for example, to improve upon a first cast iron component when creating a second cast iron component formed of the same shape. The resulting improvements in hardness obtained using the methods described herein as shown below are critical to the invention, particularly for a pump impeller as described herein, and are thus unexpected.

At step 52 of the method 50, a first cast iron component 30 a is formed into a predetermined shape. The first cast iron component 30 a can be a cast iron component 30 as illustrated in FIG. 2 and/or otherwise described herein. In an embodiment, the first cast iron component 30 a is a pump impeller 32 as illustrated in FIG. 2 and/or otherwise discussed herein.

In an embodiment, the first cast iron component 30 a is formed as discussed herein with respect to step 12 of the method 10. More specifically, the first cast iron component 30 a is formed with a first liquid mixture. The first liquid mixture can be a mixture of iron ore and one or more alloy. The first liquid mixture can contain one or more of carbon, chrome, molybdenum, nickel, manganese, silicon, sulfur, and phosphorus.

In an embodiment, the first cast iron component 30 a is stress relieved as discussed herein with respect to step 14 of the method 10.

In an embodiment, the first cast iron component 30 a is machined as discussed herein with respect to step 16 of the method 10. In an embodiment, the first component is machined at a first location for a specific purpose. In an embodiment, the first component is also machined at a second location for a specific purpose.

In an embodiment, the first cast iron component 30 a is heat treated as discussed herein with respect to step 18 of the method 10. More specifically, the first cast iron component 30 a is heat treated by raising the temperature of the first cast iron component 30 a above a first temperature for a first duration, as discussed herein. In an embodiment, the first temperature can be the upper temperature discussed herein with respect to step 18 of the method 10.

At step 54 of the method 50, the chemical composition, hardness or other property of the first cast iron component 30 a is determined. For example, the Sample 2 discussed herein was formed using steps 12 to 18 of the method 10 discussed herein. Thus, for explanation purposes, if Sample 2 was from the first cast iron component 30 a, then the chemical composition of the first cast iron component 30 a could be determined as shown in Table 3 and/or the hardness of the first cast iron component 30 a could be determined as shown in Table 4. Sample 2 could also be examined using an analysis similar to that shown with respect to FIGS. 4 and 5 and discussed herein.

TABLE 3 First Cast Iron Chemical Composition Component 30a (weight %) (Sample 2) ASTM A532 Carbon 2.1 2.0-3.3 Chrome 25.3 23-30 Molybdenum 0.4 3.0 max Nickel 0.1 2.5 max Manganese 0.4 2.0 max Silicon 0.9 1.5 max Sulphur 0.03 <0.06 Phosphorus unknown 0.10 max 

TABLE 4 First Cast Iron ASTM A532 Component 30a Hardened and (Sample 2) Stress Relieved Hardness 56.9 59 min Rockwell “C” Scale

As illustrated, the weight percentage of many of the elements of the first cast iron component 30 a are at the lower end of a range or significantly below the maximum of the ASTM A532 standard. In an embodiment, step 54 includes determining a weight percentage of at least one element of the first cast iron component 30 a to be below a predetermined value (e.g., the corresponding ASTM A532 standard value). Further, the hardness of the first cast iron component 30 a is below the minimum hardness of the ASTM A532 standard. In an embodiment, step 54 includes determining a hardness of the first cast iron component 30 a to be below a predetermined value (e.g., the corresponding ASTM A532 standard value).

In an embodiment, step 54 includes determining the martensite content of the first cast iron component 30 a. In an embodiment, step 54 includes determining the austenite content of the first cast iron component 30 a. In an embodiment, step 54 includes determining the eutectic carbides of the first cast iron component 30 a. In an embodiment, step 54 includes determining the metal carbide precipitates of the first cast iron component 30 a. As discussed above, martensite, austenite, eutectic carbides and/or metal carbide precipitates can be indicative of hardness and abrasion resistance. For example, between Samples 1 and 2 discussed herein, Sample 1 is harder and more abrasion resistant than Sample 2.

Steps 56 to 66 of the method 50 can then be used to create a second cast iron component 30 b which is identically shaped and/or machined as the first cast iron component 30 a but with an increased hardness in comparison to the first cast iron component 30 a.

At step 56 of the method 50, a second liquid mixture is created. The second liquid mixture differs from the first liquid mixture in chemical composition. Like the first liquid mixture, the second liquid mixture can be a mixture of iron ore and one or more alloy. Like the first liquid mixture, the second liquid mixture can contain one or more of carbon, chrome, molybdenum, nickel, manganese, silicon, sulfur, and phosphorus.

In an embodiment, a concentration of at least one element in the second liquid mixture is increased in comparison to the first liquid mixture. The concentration can be increased by adding at least one of carbon, molybdenum, and/or niobium to the second liquid mixture. In a preferred embodiment, niobium is added to the second liquid mixture to increase the concentration of niobium in the second liquid mixture in comparison to the first liquid mixture. In another embodiment, carbon is added to the second liquid mixture to increase the concentration of carbon in the second liquid mixture in comparison to the first liquid mixture. In another embodiment, molybdenum is added to the second liquid mixture to increase the concentration of molybdenum in the second liquid mixture in comparison to the first liquid mixture. In another embodiment, at least two of carbon, molybdenum and niobium are added to the second liquid mixture. In another embodiment, all three of carbon, molybdenum and niobium are added to the second liquid mixture.

In an embodiment, carbon is added to the second liquid mixture at step 56 when the majority of the first cast iron component 30 a is determined to be austenite at step 54. In a preferred embodiment, niobium is added to the second liquid mixture at step 56 when the first cast iron component 30 a is determined to have minimal eutectic carbide at step 54. In another embodiment, carbon is added to the second liquid mixture at step 56 when the first cast iron component 30 a is determined to have minimal martensite at step 54.

At step 58 of the method 50, a second cast iron component 30 b is formed. More specifically, the second cast iron component 30 b is formed into the predetermined shape. In an embodiment, the second cast iron component 30 b is formed as discussed herein with respect to step 12 of the method 10. The second cast iron component 30 b is formed with the second liquid mixture. In an embodiment, the second cast iron component 30 b has the same predetermined shape as the first cast iron component 30 a. The predetermined shape of the second cast iron component 30 b can be that of the cast iron component 30 as illustrated in FIG. 2 and/or otherwise described herein. In an embodiment, the second cast iron component 30 b is a pump impeller 32 as illustrated in FIG. 2 and/or otherwise discussed herein.

At step 60 of the method 50, the second cast iron component 30 b is stress relieved. In an embodiment, the second cast iron component 30 b is stress relieved as discussed herein with respect to step 14 of the method 10. In an embodiment, the second cast iron component 30 b is stress relieved at step 60 in the same manner that the first cast iron component 30 a was stress relieved at step 52.

At step 62 of the method 50, the second cast iron component 30 b is machined. In an embodiment, the second cast iron component 30 b is machined as discussed herein with respect to step 16 of the method 10. In an embodiment, the second cast iron component 30 b is machined at the same first location that the first cast iron component 30 a was machined at during step 52. In an embodiment, the second cast iron component 30 b is also machined at the same second location that the first cast iron component 30 a was machined at during step 52.

At step 64 of the method 50, the second cast iron component 30 b is heat treated. In an embodiment, the second cast iron component 30 b is heat treated as discussed herein with respect to step 18 of the method 10. More specifically, the second cast iron component 30 a is heat treated by raising the temperature of the second cast iron component 30 a above a second temperature for a second duration. In an embodiment, the second temperature can be the upper temperature discussed herein with respect to step 18 of the method 10. In an embodiment, the second temperature is less than the first temperature used for heat treatment of the first cast iron component 30 a during step 52. In an embodiment, the second duration is less than the first duration used for heat treatment of the first cast iron component 30 a during step 52. In an embodiment, both the second temperature is less than the first temperature and the second duration is less than the first duration.

In an embodiment, the second temperature and/or second duration is determined based on the determination made at step 54. In an embodiment, if the first cast iron component 30 a is determined to have minimal and/or large metal carbide precipitates at step 54, the second temperature is made to be less than the first temperature used for heat treatment of the first cast iron component 30 a during step 52. In an embodiment, if the first cast iron component 30 a is determined to have minimal and/or large metal carbide precipitates at step 54, the second duration is made to be less than the first duration used for heat treatment of the first cast iron component 30 a during step 52. In an embodiment, if the first cast iron component 30 a is determined to have minimal and/or large metal carbide precipitates at step 54, both the second temperature is made to be less than the first temperature and the second duration is made to be less than the first duration.

At step 66, the second cast iron component 30 b undergoes a cryogenic heat treatment. In an embodiment, the second cast iron component 30 b undergoes the cryogenic heat treatment as discussed herein with respect to step 16 of the method 10. More specifically, the second cast iron component 30 b undergoes a heat treatment in which the temperature of the second cast iron component 30 b is lowered to at or below a lower temperature. As discussed above, in an embodiment, the lower temperature is below 0° C., or more preferably at about −76° C. In an embodiment, the second cast iron component 30 b is maintained at below 0° C. for a duration of time. In an embodiment, the second cast iron component 30 b is maintained at between about −50° C. and −100° C., preferably between about −60° C. and −90° C., more preferably between about −70° C. and −80° C., more preferably at about −76° C. In an embodiment, the second cast iron component 30 b is maintained at this lower temperature for between about 2 to 4 hours, more preferably for about 3 hours. Thus, in an embodiment, the second cast iron component 30 b is maintained at about −76° C. for 3 hours.

Table 6 illustrates how the hardness of the second cast iron component 30 b improved in comparison to the first cast iron component 30 a using the method 50. In Table 6, the hardness was increased from 56.9 to 59 by adding niobium to the chemical composition while staying in line with the higher end of the ASTM A532 Grade 3 ranges. This brought the hardness of the second cast iron component 30 b in line with the ASTM A532 standard. This also created an unexpected result in that the hardness of 59 could be achieved by only adding niobium to the previous chemical composition. The hardness of the second cast iron component 30 b was further increased from 59 to 61 by performing the cryogenic heat treatment at step 66. This further raised the hardness of the second cast iron component 30 b above the minimum ASTM A532 standard. The increased hardness leads to durability and increased run time, which reduces product failures and replacements in this field.

TABLE 6 ASTM A532 First Cast Iron Hardened Component 30a Second Cast Iron and Stress (e.g., Sample 2) Component 30b Relieved Hardness 56.9 59 min Rockwell “C” Scale (determined at step 54) Hardness 59 59 min Rockwell “C” Scale (before step 66) Hardness 61 59 min Rockwell “C” Scale (after step 66)

The methods described herein can be used to create new cast iron components with desirable hardness and/or to improve the hardness of cast iron components made with existing molds and/or machining tools. It should be understood that various changes and modifications to the methods described herein will be apparent to those skilled in the an and can be made without diminishing the intended advantages.

General Interpretation of Terms

In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts.

While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, the size, shape, location or orientation of the various components can be changed as needed and/or desired. Components that are shown directly connected or contacting each other can have intermediate structures disposed between them. The functions of one element can be performed by two, and vice versa. The structures and functions of one embodiment can be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such features. Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 

What is claimed is:
 1. A method of forming a cast iron component for industrial equipment, the method comprising: forming the cast iron component in a predetermined shape; machining the cast iron component; heat treating the cast iron component by raising the temperature of the cast iron component to an upper temperature; and cryogenically heat treating the cast iron component by lowering the temperature of the cast iron component to a lower temperature.
 2. The method of claim 1, wherein the lower temperature is at or below 0° C.
 3. The method of claim 1, wherein the upper temperature is at or above 950° C.
 4. The method of claim 1, wherein cryogenically heat treating the cast iron component includes lowering the temperature of the cast iron component to between about −70° C. and −80° C.
 5. The method of claim 1, wherein cryogenically heat treating the cast iron component includes maintaining the cast iron component at about the lower temperature for between about 2 to 4 hours.
 6. The method of claim 1, including stress relieving the cast iron component before machining the cast iron component;
 7. The method of claim 1, wherein forming the cast iron component includes forming the cast iron component as a single piece.
 8. The cast iron component formed using the method of claim
 1. 9. A pump impeller formed as the cast iron component using the method of claim
 1. 10. A method of improving the hardness cast iron components for industrial equipment, the method comprising: forming a first cast iron component into a predetermined shape using a first liquid mixture, the first cast iron component having a first hardness; increasing a concentration of at least one element in a second liquid mixture in comparison to the first liquid mixture; forming a second cast iron component into the predetermined shape using the second liquid mixture, the second cast iron component having a second hardness greater than the first hardness; and further increasing the second hardness of the second cast iron component by cryogenically heat treating the second cast iron component by lowering the temperature of the cast iron component to a lower temperature.
 11. The method of claim 10, wherein the at least one element is carbon.
 12. The method of claim 10, wherein the at least one element is molybdenum.
 13. The method of claim 10, including adding niobium to the second liquid mixture.
 14. The method of claim 10, including heat treating the first cast iron component by raising the temperature of the first cast iron component to a first temperature for a first duration, and heat treating the second cast iron component by raising the temperature of the second cast iron component to a second temperature for a second duration, the second temperature being lower than the first temperature.
 15. The method of claim 10, including heat treating the first cast iron component by raising the temperature of the first cast iron component to a first temperature for a first duration, and heat treating the second cast iron component by raising the temperature of the second cast iron component to a second temperature for a second duration, the second duration being less than the first duration.
 16. The method of claim 10, including machining the first cast iron component at a first location, and machining the second cast iron component at the first location.
 17. The second cast iron component formed using the method of claim
 10. 18. A pump impeller formed as the second cast iron component using the method of claim
 1. 19. A method of improving the hardness cast iron components for industrial equipment, the method comprising: forming a first cast iron component into a predetermined shape using a first liquid mixture; heat treating the first cast iron component by raising the temperature of the first cast iron component to a first temperature for a first duration, the first cast iron component having a first hardness after heat treatment; forming a second cast iron component into the predetermined shape using a second liquid mixture; heat treating the second cast iron component by raising the temperature of the second cast iron component to a second temperature for a second duration, the second cast iron component having a second hardness after heat treatment, the second hardness greater than the first hardness, at least one of the second temperature being lower than the first temperature and/or the second duration being less than the first duration; and further increasing the second hardness of the second cast iron component by cryogenically heat treating the second cast iron component by lowering the temperature of the cast iron component to a lower temperature.
 20. The method of claim 19, including increasing a concentration of at least one element in a second liquid mixture in comparison to the first liquid mixture. 